Cities with the most millionaires per capita

One out of every 22 New Yorkers is a millionaire, according to a study.

WealthInsight and Spear's looked at which cities have the highest percentage of millionaires, also known as millionaire density. Not surprisingly, the sovereign city-state Monaco had the highest percentage of millionaires. Nearly one in three people in Monaco is a millionaire (and the rest work for them).

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"It's unsurprising to see that Monaco is the most likely place where you will bump into a millionaire; the principalities' low tax and Mediterranean waterfront is the ideal habitat for wealthy individuals," said WealthInsight Analyst Oliver Williams.

Monte Carlo, Monaco
Brian Lawrence | Photographer's Choice | Getty Images

Switzerland's Zurich and Geneva ranked second and third, proving that millionaires love a good tax break more than cultural diversity.

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The top-ranked city in the U.S. was New York, with 4.63 percent. The other two U.S. cities that made the top 20 list are Houston and San Francisco.

Here is the full list:

Top 20 global cities by millionaire density

1 Monaco 29.21%
2 Zurich 27.34%
3 Geneva 17.92%
4 New York 4.63%
5 Frankfurt 3.88%
6 London 3.39%
7 Oslo 2.90%
8 Singapore 2.80%
9 Amsterdam 2.63%
10 Florence 2.59%
11 Hong Kong 2.58%
12 Rome 2.54%
13 Dublin 2.40%
14 Doha 2.31%
15 Toronto 2.29%
16 Venice 2.25%
17 Brussels 2.11%
18 Houston 2.09%
19 San Francisco 2.07%

Source: Source: WealthInsight and Spears

—CNBC's Robert Frank